The present invention relates to a detector for radon concentrations and, in particular, it relates to a radon detector having a tortuous channel for entry of radon into the detector.
Radon (.sup.222 Rn) is a heavy, radioactive, zerovalent gaseous element in Group O (inert gases) of the periodic table formed as a gaseous emanation from the radioactive decay of radium. The element is highly radioactive and has a half-life of 3.823 days. Radon decays by the emission of energetic alpha particles. All known isotopes from radon 204 to radon 224 are radioactive with short half-lives.
Generally, exposure to the radioactive emissions of radon is not dangerous to normal human skin. However, if the soft tissue of the human body is exposed to these radioactive emissions, damage can occur. Therefore, since any surface (including dust particles) exposed to radon becomes coated with an active deposit consisting of a group of short-lived daughter products, it is important to monitor the amount of radon in any given environment, including homes and work places. If radon attaches to dust particles and these particles are inhaled, then the lungs of the person which inhaled the radon contaminated dust particles will be exposed to potentially damaging radiation exposure.
Another isotope of radon is an alpha particle emitter known as .sup.220 Rn or thoron. Although exposing soft tissue to thoron emissions is also potentially harmful, thoron has a half-life of only 54.5 seconds. Such a short half-life reduces the risk of any dangerous effect of thoron.
Typically, radon monitoring techniques are carried out by placing one or more housings, each containing a strip of track registration material, in locations to be monitored (such as a mine or a dwelling), and permitting the detectors to remain at the monitored site for a preselected period of time, i.e., several weeks. After exposure, the housings are removed, the track registration material is subjected to a chemical etching solution, and the number of tracks etched per unit area on each strip is counted by microscopic inspection. The thus-obtained track data is then used to compute the average radon concentration at a monitored site.
Patents that describe detectors for radon and radon daughter products include Alter et al U.S. Pat. 4,518,860 and Urban et al U.S. Pat. No. 4,704,537. The Alter et al patent describes a detector for radon and radon daughter products having a housing with a removable closure cap for retaining a strip of track registration material. The strip is retained within the housing by upstanding ribs located closely adjacent diametrically opposed inner side wall portions of the housing. A microporous filter covers the interior of the housing. The cap has a central solid portion providing a radiation shield for the upper surface of the strip to enable the lower exposure surface to be distinguished after the detector has been retrieved from an exposure site.
The Urban et al patent describes a passive dosimeter including a diffusion chamber and an alpha particle detector located within the chamber. The diffusion chamber is constructed so that the interior is open to the outside. The size of the detector and the interior space are selected for causing the differences in path length of alpha particles and the interior space to permit the emission energy to be determined independently of the location decay events.